Method for coating metallic interconnect of solid fuel cell

ABSTRACT

Disclosed herein is a method for coating a metallic interconnect of a solid oxide fuel cell. The method for coating a metallic interconnect of a solid oxide fuel cell includes generating a cobalt compound solution using lithium cobalt oxide (LiCoO 2 ) that is an anodic material of a lithium ion battery; immersing the metal interconnect in a plating solution in which the generated cobalt compound solution is contained; and forming cobalt (Co) on the immersed metal interconnect by performing electroplating.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2011-0097742, filed on Sep. 27, 2011, entitled “Method For Coating Metallic Interconnect Of Solid Oxide Fuel Cell”, which is hereby incorporated by reference in its entirety into this application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method for coating a metallic interconnect of a solid oxide fuel cell.

2. Description of the Related Art

Due to the depletion of fossil fuel, new renewable energy related industries have been in the limelight.

Among others, a fuel cell, which may replace the existing fossil fired power plant, can achieve higher energy efficiency, reduce sulfur oxides and carbon emissions. For this reason, various researches into the fuel cell have been conducted. In the case of the fuel cell, the continuous power generation may be performed under the assumption that fuel is continuously supplied. Therefore, the fuel cell has less temporal and spatial limitations as compared with other new energy technologies.

The fuel cell is an apparatus that directly converts chemical energy of fuel (hydrogen, LNG, LPG, or the like) and air (oxygen) into electricity and heat by an electrochemical reaction. The power generation technologies according to the prior art need to perform processes such as fuel combustion, vapor generation, turbine driving, generator driving, or the like. On the other hand, the fuel cell does not perform the processes of the fuel combustion or the turbine driving and therefore, is a new conceptual power generation technology that does not induce environmental problems while increasing efficiency.

The fuel cell emits little air pollutants such as SO_(x), NO_(x), or the like, can achieve pollution-free power generation due to the reduced generation of carbon dioxide, and can achieve low noise, non-vibration, or the like.

As an example of the fuel cell, there may be various types such as a phosphoric acid fuel cell (PAFC), an alkaline fuel cell (AFC), a polymer electrolyte membrane fuel cell (PEMFC), a direct methanol fuel cell (DMFC), a solid oxide fuel cell (SOFC), or the like. Among others, the solid oxide fuel cell (SOFC), which is a fuel cell having a ceramic-base solid electrolyte, is operated at an operation temperature higher than that of other fuel cells, that is, 700 to 1000° C., such that the SOFC may increase conductivity of an electrolyte to implement high efficiency and use waste heat of high temperature to implement a hybrid power generation system.

Meanwhile, the solid oxide fuel cell may be largely sorted into a flat type and a tubular type.

The flat type solid oxide fuel cell according to the prior art is disclosed in Korean Patent No. 0341402 and a cylindrical solid oxide fuel cell among the tubular solid oxide fuel cells is disclosed in Korean Patent No. 0344936.

Generally, the solid oxide fuel cell (SOFC) includes a metallic interconnect that electrically connects an anode of one cell and cathodes of adjacent cells and serves to physically interrupt fuel gas from air gas.

In the solid oxide fuel cell (SOFC), an example of several alloys used until now as the metallic interconnect may largely include Cr-base alloy based on Cr, ferritic Fe—Cr alloy based on Fe, and Ni-base alloy based on Ni, or the like.

In the solid oxide fuel cell operated at an operation temperature of 800° C. or less, among those, the ferritic Fe—Cr alloy is more advantageous in terms of workability that the chromium-base alloy or the Ni-base alloy.

However, these alloys are very expensive and generate volatile chromium (Cr) under the high-temperature operation environment. As described above, the chromium (Cr) is diffused to the cathode, which is a serious factor of hindering the normal electrochemical reaction of the fuel cell and reducing the performance thereof.

Meanwhile, stainless steel is more inexpensive than the ferritic Fe—Cr alloy and may form a large amount of oxide at high temperature while volatizing the chromium (Cr) contained therein, such that the stainless steel cannot be used as an interconnect of the fuel cell until now.

As described above, a protective layer having a function of oxidation resistance and preventing chromium from being volatized is formed on the surface of the stainless steel, such that the stainless steel can secure oxidation stability in the long term. As a result, it is highly likely for the stainless steel to be used as the metallic interconnect having excellent conductivity at low cost.

SUMMARY OF THE INVENTION

The present has been made in an effort to provide a method for coating a metallic interconnect of a solid oxide fuel cell capable of preventing chromium (Cr) from being volatized at high temperature.

In addition, the present invention has been made in an effort to provide a method for coating a metallic interconnect of a solid oxide fuel cell capable of securing oxidation stability at high temperature.

Further, the present invention has been made in an effort to provide a method for coating a metallic interconnect of a solid oxide fuel cell capable of using a low-cost material as a metallic interconnect having excellent oxidation resistance and conductivity.

According to a preferred embodiment of the present invention, there is provided a method for coating a metallic interconnect of a solid oxide fuel cell, including: generating a cobalt compound solution using lithium cobalt oxide (LiCoO₂) that is an anodic material of a lithium ion battery; immersing the metal interconnect in a plating solution in which the generated cobalt compound solution is contained; and forming cobalt (Co) on the immersed metal interconnect by performing electroplating.

The cobalt compound may be cobalt sulfate (CoSO₄).

The generating of the cobalt compound solution may be performed by dissolving the lithium cobalt oxide (LiCoO₂) with a sulfuric acid solution (H₂SO₄).

The metallic interconnect may be made of ferritic stainless steel.

The forming of the cobalt (Co) on the metallic interconnect may include: immersing a cobalt plate in the plating solution; connecting a cathode to the immersed metallic interconnect and connecting an anode to the cobalt plate; and performing electroplating by applying current.

The method for coating a metallic interconnect of a solid oxide fuel cell may further include pre-treating removing impurities on a surface of the metal interconnect prior to immersing the metal interconnect in the cobalt compound (CoSO₄) solution.

The pre-treating may be performed by a mechanical polishing process and a washing process using a washing solution.

The method for coating a metallic interconnect of a solid oxide fuel cell may further include oxidizing the cobalt (Co) with the cobalt oxide (Co₃O₄) by performing heat treatment on the metallic interconnect after the forming of the cobalt (Co) on the metallic interconnect.

The plating solution may be made of the cobalt compound solution and distilled water.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the U.S. Patent and Trademark Office upon request and payment of the necessary fee.

FIG. 1 is a flow chart showing a method for coating a metallic interconnect of a solid oxide fuel cell according to a preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view showing a cross section of a metallic interconnect having cobalt oxide (Co₃O₄) formed on a surface of thereof by a method for coating a metallic interconnect of a solid oxide fuel cell according to the preferred embodiment of the present invention; and

FIG. 3 is a graph showing conductivities between the metallic interconnect formed by the method for coating a metallic interconnect of a solid oxide fuel cell according to the preferred embodiment of the present invention and the metallic interconnect formed by the method for coating a metallic interconnect of a solid oxide fuel cell according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various objects, advantages and features of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

The terms and words used in the present specification and claims should not be interpreted as being limited to typical meanings or dictionary definitions, but should be interpreted as having meanings and concepts relevant to the technical scope of the present invention based on the rule according to which an inventor can appropriately define the concept of the term to describe most appropriately the best method he or she knows for carrying out the invention.

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. In the specification, in adding reference numerals to components throughout the drawings, it is to be noted that like reference numerals designate like components even though components are shown in different drawings. Further, when it is determined that the detailed description of the known art related to the present invention may obscure the gist of the present invention, the detailed description will be omitted. Terms used in the specification, ‘first’, ‘second’, etc. can be used to describe various components, but the components are not to be construed as being limited to the terms. The terms are only used to differentiate one component from other components.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a flow chart showing a method for coating a metallic interconnect of a solid oxide fuel cell according to a preferred embodiment of the present invention.

Referring first to FIG. 1, a cobalt compound solution is generated by using lithium cobalt oxide (LiCoO₂) that is an anodic material of a lithium ion battery (S101).

Generally, since the lithium ion battery has high energy density and lightness characteristics, the lithium ion battery has been used as a power supply of small portable equipment. In recent years, a use of the lithium ion battery has been rapidly increased.

In the lithium ion battery, a unit cell is configured to have an anode in which the anodic material, that is, lithium cobalt oxide (LiCoO₂) is applied to a current collector metallic plate, that is, an aluminum plate, a cathode in which cathodic materials such as graphite, carbons, or the like, are applied to the current collector metal plate, that is, a copper plate, and an organic electrolytic solution in which an organic separator and a lithium salt are dissolved. One unit cell or a combination of several unit cells is packaged with plastic, together with a charging protective integrated circuit chip.

Even though the lithium ion battery configured as described above can be charged and discharged and has a relatively long lifespan, the lithium ion battery is consumed goods having a limited lifespan. Therefore, wastes have been increased with the increase in consumption.

The waste lithium ion battery has a large amount of valuable metals, such as lithium (Li), cobalt (Co), or the like, while having simple gradients and therefore, is recognized as waste resources having an economic value.

According to the preferred embodiment of the present invention, generating the cobalt compound solution from the waste lithium ion battery may be made as follows, but the preferred embodiment of the present invention is not particularly limited thereto.

First, after the waste lithium ion battery is prepared and plastic forming an appearance of the waste lithium ion battery is fragmented and removed, an electrode material is recovered.

In this case, an example of the electrode material may include lithium (Li), cobalt (Co), or the like, that are used as the anodic and cathodic materials.

Next, the cathodic materials, conductors, and binders, which are included in the electrode material, are removed by performing heat treatment on the electrode materials and the anodic material, that is, the lithium cobalt oxide (LiCoO₂) is recovered.

That is, graphite used as the cathodic material, carbon used as the conductor, and polymer materials used as the binder are removed from an electrode material powder separated by the above-mentioned heat treatment. In this case, the heat treatment may be performed twice at 700° C. and 900° C. by using an atmosphere furnace (gas atmosphere pipe), but the preferred embodiment of the present invention is not particularly limited thereto.

Next, the cobalt compound solution is generated by reacting the recovered lithium cobalt oxide (LiCoO₂) with sulfuric acid solution (H₂SO₄).

According to the above-mentioned processes, in the preferred embodiment of the present invention, the lithium cobalt oxide (LiCoO₂) may be extracted from the waste lithium ion battery and the cobalt compound solution may be obtained from the extracted lithium cobalt oxide (LiCoO₂).

In this case, the cobalt compound may be cobalt sulfate (CoSO₄).

Next, the metallic interconnect is immersed in a plating solution including the acquired cobalt compound (CoSO₄) solution (S103).

In the preferred embodiment of the present invention, an example of the metallic interconnect may include ferritic stainless steel, for example, SUS430, or the like, but the preferred embodiment of the present invention is not particularly limited thereto.

In this case, before the metallic interconnect is immersed in the plating solution, a pretreatment process of removing impurities attached to the surface of the metallic interconnect may be performed.

In this case, the pretreatment process may be performed as follows, but the preferred embodiment of the present invention is not limited thereto.

First, the surface of the metallic interconnect is polished using silicon carbide (SiC) abrasive paper (for example, abrasive paper having roughness No. #100 to 2000).

Next, the impurities attached to the surface of the metallic interconnect are washed with 10% of aqueous sodium hydroxide (NaOH) solution and acetone. Next, a fine scale on the surface of the metallic interconnect is removed with 10% of hydrogen chloride (HCl) solution and then, pickling is performed for 30 to 60 seconds.

The metallic interconnect subjected to the pretreatment process as described above is immersed in a bath in which the plating solution is contained.

In this case, the plating solution may be a solution in which the cobalt sulfate (CoSO₄) solution and distilled water are mixed, but the preferred embodiment of the present invention is not particularly limited thereto.

For example, the plating solution may be added with, as additives, various gradients that may derive desired effects, such as an additive for making a plating thickness uniform, an additive for reducing pit density, or the like.

Next, the protective layer made of cobalt (Co) is formed on the surface of the metallic interconnect by performing electroplating (S105).

In the preferred embodiment of the present invention, the process of forming the protective layer made of cobalt (Co) on the metallic interconnect may include the following processes.

First, a cobalt plate is immersed in a plating solution bath in which the metallic interconnect is immersed.

Next, the metallic interconnect is connected to the cathode, the cobalt plate is connected to the anode, and then, the electroplating is performed by applying current.

As described above, the cobalt (Co) ions generated in the plating solution are attached to the surface of the metallic interconnect by performing the electroplating, such that the protective layer made of cobalt (Co) may be formed on the metallic interconnect.

In the preferred embodiment of the present invention, the metallic interconnect in which the protective layer made of Co is formed on the surface of the metallic interconnect according to the above-mentioned process is exposed to air and is subjected to heat treatment at high temperature to oxidize the cobalt (Co) with the cobalt oxide (Co₃O₄), thereby improving the oxidation stability of the protective layer and increasing the adhesion between the protective layer and the metallic interconnect.

In this case, the heat treatment may be performed within a range of 200° C. to 800° C., but the preferred embodiment of the present invention is not particularly limited thereto.

Hereinafter, the preferred embodiment of the present invention will be described with reference to the following examples but the scope of the preferred embodiment of the present invention is not limited to the following examples.

The plating solution is prepared by dissolving the cobalt sulfate (CoSO₄-7H₂0) having purity of 95% in 500 ml of distilled water, wherein the cobalt sulfate is separated by dissolving the anodic material of the waste lithium ion battery, that is, the lithium cobalt oxide (LiCoO₂) using the sulfuric acid solution (H₂SO₄).

After immersing the cobalt plate as the anode material in the plating solution and the metallic interconnect (SUS430) as the cathode material therein, the electroplating is performed for 30 minutes by applying current with a current density of 50 mA/cm², thereby coating the surface of the metallic interconnect with cobalt (Co).

After the electroplating is performed, the heat treatment was performed on the metallic interconnect at an atmosphere temperature of 200° C.

According to the above-mentioned processes, the cross section of the metallic interconnect 200 on which the protective layer 210 made of the cobalt oxide (Co₃O₄) is formed is shown in FIG. 2.

In addition, the conductivity of the protective layer 210 made of the cobalt oxide (Co₃O₄) formed on the surface of the metallic interconnect 200 was measured. The measurement was performed after the metallic interconnect is exposed for 100 hours at an atmosphere temperature of 800° C. and the measured results were shown by a graph in FIG. 3.

As shown in FIG. 3, in the case of the metallic interconnect (Co-SUS 430) according to the preferred embodiment of the present invention, a resistance value of 0.1 Ω/cm² or less was obtained.

For the comparison, the conductivity for a crofer alloy (crofer 22 APU) and ferrotherm alloy that were used as the metallic interconnect in the prior art was measured under the same conditions. However, similar to FIG. 3, the resistance value higher than that of the metallic interconnect (Co-SUS 430) according to the preferred embodiment of the present invention was measured.

Referring to FIG. 3, it could be appreciated that the conductivity of the metallic interconnect according to the preferred embodiment of the present invention is more excellent than that of the metallic interconnects.

As set forth above, the preferred embodiment of the present invention can suppress the generation and volatilization of chromium while securing the oxidation stability by forming a protective layer made of cobalt oxide (Co₃O₄) on the surface of the metallic interconnect to prevent the pollution of the cathode, thereby improving the performance and the durability of the solid oxide fuel cell.

In addition, the preferred embodiments of the present invention can form the protective layer made of cobalt oxide (Co₃O₄) on the metallic interconnect by using the cobalt compound (CoSO₄) acquired from the waste lithium secondary battery, thereby reducing the manufacturing costs of the fuel cell.

In addition, the preferred embodiments of the present invention can use the low-cost material as the metallic material having the excellent oxidation resistance and conductivity at the high temperature by forming the protective layer made of the cobalt oxide (Co₃O₄) on the surface of the low-cost stainless steel.

Although the embodiment of the present invention has been disclosed for illustrative purposes, it will be appreciated that a method for coating metallic interconnect of solid oxide fuel cell according to the invention is not limited thereto, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention.

Accordingly, any and all modifications, variations or equivalent arrangements should be considered to be within the scope of the invention, and the detailed scope of the invention will be disclosed by the accompanying claims. 

What is claimed is:
 1. A method for coating a metallic interconnect of a solid oxide fuel cell, comprising: generating a cobalt compound solution using lithium cobalt oxide (LiCoO₂) that is an anodic material of a lithium ion battery; immersing the metal interconnect in a plating solution in which the generated cobalt compound solution is contained; and forming cobalt (Co) on the immersed metal interconnect by performing electroplating.
 2. The method as set forth in claim 1, wherein the cobalt compound is cobalt sulfate (CoSO₄).
 3. The method as set forth in claim 1, wherein the generating of the cobalt compound solution is performed by dissolving the lithium cobalt oxide (LiCoO₂) with a sulfuric acid solution (H₂SO₄).
 4. The method as set forth in claim 1, wherein the metallic interconnect is made of ferritic stainless steel.
 5. The method as set forth in claim 1, wherein the forming of the cobalt (Co) on the metallic interconnect includes: immersing a cobalt plate in the plating solution; connecting a cathode to the immersed metallic interconnect and connecting an anode to the cobalt plate; and performing electroplating by applying current.
 6. The method as set forth in claim 1, further comprising pre-treating removing impurities on a surface of the metal interconnect prior to immersing the metal interconnect in the cobalt compound (CoSO₄) solution.
 7. The method as set forth in claim 6, wherein the pre-treating is performed by a mechanical polishing process and a washing process using a washing solution.
 8. The method as set forth in claim 1, further comprising oxidizing the cobalt (Co) with the cobalt oxide (Co₃O₄) by performing heat treatment on the metallic interconnect after the forming of the cobalt (Co) on the metallic interconnect.
 9. The method as set forth in claim 1, wherein the plating solution is made of the cobalt compound solution and distilled water. 